You register 10 (non-private) inputs, and 1 of them gets rejected, what is your conclusion? To me, absolutely none. Coinfirm might have deemed this one input as inappropriate, or it might be trying to get rid of some coinjoin inputs, so they can use theirs instead and de-anonymize the remaining registered inputs. For instance, a 150-input long coinjoin can have its 75 inputs rejected, and replaced with 75 Coinfirm inputs. That leaves the firm with 50% less output set to account for.